1. Field of the Invention
This invention relates to a method for driving a display panel in which are arranged light emission (hereinafter, simply referred to as “emission”) elements having only two states, emitting and non-emitting.
2. Description of the Related Art
With the rend toward display device with larger screens in recent years, displays with thinner shapes have been sought. AC-discharge type plasma display panels have attracted attention as one thin-type display device.
FIG. 1 shows in summary the configuration of a plasma display device equipped with such a plasma display panel.
In FIG. 1, the plasma display panel PDP 10 comprises m column electrodes D1 to Dm, as data electrodes, and n row electrodes X1 to Xn and Y1 to Yn, arranged to intersect each of the column electrodes. Each of the pairs X and Y of row electrodes corresponds to a row of the screen. These column electrodes D and row electrodes X and Y are formed on two glass substrate s, arranged in opposition and enclosing a discharge space into which is injected a discharge gas. At the portions of intersection of each of the row electrodes and column electrodes, discharge cells serving as display elements corresponding to individual pixels are formed.
Because the discharge cells utilize a discharge phenomenon, they have only two states, “emitting” and “non-emitting”. That is, discharge cells are capable of representing only the brightnesses of two grayscales, at the minimum brightness (the non-emitting state) and at the maximum brightness (the emitting state). The driving device 100 executes grayscale driving of the above PDP 10, in which such discharge cells are arranged in a matrix shape, using a subfield method in which intermediate grayscale brightnesses corresponding to input image signals are represented.
In the subfield method, the display interval for one subfield is divided into, for example, eight subfields SF1 to SF8, as shown in FIG. 2. To each of these subfields SF1 to SF8 is allocate d a number of times emission is to be executed within that subfield. Hence by changing the combination of the subfields during which emission is executed and the subfields during which emission is not executed based on the input image signal, emission is executed, within the display interval of one field, a number of times corresponding to the brightness level of the input image signal. As a result, an intermediate brightness is perceived corresponding to the total number of emissions executed within the field display interval in question.
FIG. 3 is a figure showing one example of emission driving pattern is, indicating combinations of subfields for which emission is executed and subfields for which emission is not executed.
The driving device 100 selects one emission driving pattern from among the nine types shown in FIG. 3, according to the input image signal. The different driving pulses are applied to the column electrodes D and row electrodes X and Y of the PDP 10 so as to execute emission for the number of times shown in FIG. 2 only in those subfields indicated by white circles in the selected emission driving pattern.
Through the nine types of emission driving patterns shown in FIG. 3, images can be displayed having nine intermediate brightnesses, with emission brightness ratios of 0, 1, 7, 23, 47, 82, 128, 185, and 255.
Here, by means of the emission driving patterns shown in FIG. 3, after first putting a discharge cell in the non-emitting state in one subfield within a field interval, emission is not executed again in subsequent subfields. That is, as indicated by the white circles, emission driving patterns wherein subfields in which emission is executed continuously (hereafter called the “continuous emission state”) and subfields in which the extinguished state is continuous (hereafter called the “continuous extinguished state”) alternate within a single field interval are excluded. As a result, so-called false contours, occurring on the boundaries of two image regions in which the above continuous emission state and the above continuous extinguished state alternate, is suppressed.
In an emission driving pattern like that shown in FIG. 3, the frequency of switching between the above continuous emission state and the above continuous extinguished state is equal to the vertical sync frequency which determines the display interval for a single field. Hence there is concern that when a PAL television signal, which has only a 50 Hz vertical sync frequency, may be supplied as the input image signal, and when the brightness levels represented by this image signal are comparatively high, flicker may occur.